About ~6 months ago I built my PC, and recently there has been a problem with what I suspect to be the GPU fan. So far it's happened twice with about a 3 or 4 day interval. What happens is, my monitor goes completely blank, sound starts skipping, and the GPU makes a high pitched whirring noise. The computer pretty much locks up. I can't turn it off, so I have to manually unplug it from the wall. I'm hoping someone can help me with this problem?